1. Field of the Invention
The present invention relates to a reclosing device for a three-phase transmission line interrupted by a circuit breaker during a current fluctuation and, more particularly, to a reclosing circuit which recloses a particular terminal of the transmission line in association with the success or failure of reclosing other terminals.
1. Description of the Prior Art
As is well known, a transmission line is broken by a circuit breaker when a fault such as a ground-fault, short-circuiting, or a flashover is caused in the transmission line. When the breaking has been caused by the flashover, for example, power transmission may be continued without any problem upon reclosing the circuit after a predetermined period of time. Therefore, this reclosing is extremely effective for improving the transmission stability and for increasing the quantity of power transmitted. When a fault section is broken and the operation of this section is not restarted, the stability of the power system is lowered. When a second or third fault is caused under this condition, the stability may decay. It is, thus, important with the transmission line to quickly reclose the circuit after the breaking due to the fault. This particularly applies to the case of abnormal weather conditions such as lightning under which faults are liable to happen.
However, a reclosing may not always be accomplished successfully. When the cause of the fault at the place of the fault has not been removed, the fault will happen again immediately after the reclosing, thus breaking the circuit again. When the fault happens again, supply of power through the line in the vicinity of the fault becomes difficult and extreme power instability results. The output of a power generator alters from the rated load to a no-load condition and is then restored to the rated load condition. This causes significant stress between the shafts of the generator and a motor. When the fault happens a second time after the reclosing, the power instability and the stress between the shafts due to the first fault is reinforced by the additional power instability and stress between the shafts. This significantly adversely affects the power system and tends to cause stability decay of the power system, damage due to excessive stress between the shafts and so on.